As this kind of roll screen device, a structure described in Japanese Unexamined Patent Publication No. 2001-107666 has been conventionally known. This roll screen device is structured such that a screen is taken up by a take-up shaft, an inner rail is embedded into an inner portion of each of a pair of opposed guide rails which guide a movement of both side edge portions of the screen taken out of the take-up shaft, the inner rail is provided with a guide groove to which a guide protrusion provided along both side edge portions of the screen and being capable of being taken up spirally is movably inserted, a pair of inward flanges are formed in an opening end portion of the guide groove, and the guide protrusion is slid and guided in a come-off preventing state by a pair of inward flanges.
In the roll screen device as mentioned above, in general, a fastener tape in a slide fastener is overlapped with a side edge portion of the screen so as to be firmly fixed by a high frequency welder, and a fastener element which is provided along one side edge of the fastener tape is set to the guide protrusion.
In the roll screen device as mentioned above in which the fastener element is set to the guide protrusion, in the case where a thickness of the fastener element serving as the guide protrusion is thicker than a thickness of the screen, in the spirally winding state of the screen by the take-up shaft, the guide protrusions overlap with each other and winding diameters of both end portions become larger than a winding diameter of a center portion, whereby the screen is taken up like a double headed conical shape and a crease is generated in both end portions, or the guide protrusion is taken up so as to be displaced in a width direction of the screen with respect to the previously taken up guide protrusion and the screen winds its way, so that a resistance at a time of taking up becomes great, and it is impossible to smoothly take up.
In order to solve the problem mentioned above in the roll screen device described in Japanese Unexamined Patent Publication No. 2001-107666, the thickness of the screen is made thicker than the thickness of the guide protrusion, thereby preventing the guide protrusions from being taken up in an overlapping manner.
In the meantime, in the conventional roll screen device, since the thickness of the screen is made thicker than the thickness of the guide protrusion although the screen can be extremely finely taken up, the screen comes to a heavy load, and can not be smoothly taken up while requiring great operating force for taking up. Further, if the screen is long, the roll screen device must be large in size, and an applicable range of the roll screen device becomes narrow, so that there is left a point to be improved on an expansion of the applicable range.
In this case, in recent years, as the fastener tape, a structure in which the tape thickness is about 0.35 mm, and the fastener element set to the guide protrusion is extremely thin about 1.0 mm has developed and is going to be produced. The inventor of the subject case has found that a clean take-up state can be obtained without enlarging a winding diameter in both end portions even in the thin screen by employing the extremely thin fastener tape as mentioned above, and has intended to employ the fastener tape for the roll screen device, but could not employ it due to the following problems.
In other words, the inner rail which guides the movement of the fastener element serving as the guide protrusion is formed of molded synthetic resin, a gap which guides the movement of the fastener tape is provided between opposed portions of the pair of inward flanges, in an inner portion in which the inward flanges are formed, no gap exists in an outer portion in an opposite side, and the outer portion of the inner rail contracts so as to be curved in a width direction after being formed, due to the presence/absence of the gap. Further, since an amount of contraction is not uniform, it is impossible to absolutely secure a guide gap having such a size that can prevent the fastener element from coming off, more particularly, a guide gap of about 0.7 mm, between the opposed surfaces of the pair of inward flanges.
Therefore, if tensile force directed to an inner side in a width direction is applied to the screen at a time of inserting the guide protrusion into the guide grove formed in the inner rail, and sliding and guiding the guide protrusion by the pair of the inward flanges, the guide protrusion gets out of the gap between the pair of inward flanges, and it is impossible to prevent the guide protrusion from coming off.